Even easier put a single diode between the 2 coils on the factory (lo beam & hi beam) relays. Buy a 3 amp diode, solder a red wire to the Anode and a black wire to the cathode, cover in heat shrink. Open relay box under the bonnet and pull the Hi Beam & Lo Beam relays out. The relays are energized by switching the earth. With a multimeter find which connection on the Hi Beam relay connector is the one giving earth to the relay coil (sorry can't remember the number on the relay), connect the Cathode of the diode (black wire) to this connector I just jammed the wire into the connector when I put the relay back in. Connect the Anode (red wire) of the Diode to the earth connector on the lo beam relay coil. Now when you hit the hi beam the lo beam will stay energised coz the diode will suppy the earth to the lo beam relay. uses bugger all power also.